Abstract: The effects of the alumina doped through the normal co-precipitation on the sintering and conductivity of
Yttria-stabilized zirconia were studied. The study shows that proper addition of alumina can accelerate the process of sintering and improve the
sintering density of zirconia, but it does harm to the sintering density of YSZ if the content of alumina is too high; the grain-boundary conductivity
increases at first and then decreases with increasing content of added alumina. The reason why grain-boundary conductivity changes with the content of alumina
is that alumina segregated to the grain boundary has two opposite effects on the grain boundary: at one side it can scavenge silicon dioxide which blocks
ionic transport at the grain boundary, at the other side it decreases the free oxygen ion vacancy concentration.

Key words: zirconia, alumina, oxygen ion vacancy, space charge layer